Conventionally, different kinds of communication systems are used to provide voice, data, and video communication services to subscribers. In particular, interactive cable television systems have been developed to distribute information to subscriber's televisions at their requests. One such system concerns a shopping service where subscribers shop at home in an "electronic mall". This system is distinguished from home shopping channels since it allows subscribers to select which products or services they will view on their television screens by use of in-house subscriber apparatus, such as telephones or CATV key pads. In operation, the subscriber tunes to a channel and requests connection to a remote location by dialing a predetermined telephone number, or accesses via a CATV reverse channel. As soon as the system identifies the subscriber, his television screen begins to display still-frame video, and possibly accompanying audio, and directories of "electronic stores" comprising products or services that may be entered or passed, examined in further detail, saved for future consideration, or purchased just by touching keys on a touch-tone telephone in response to prompts on the television screen. A main-frame host computer controls the flow of information in the system.
This shopping service uses a CATV network to distribute the video presentations and accompanying audio messages requested by subscribers. At various locations in the CATV network, a device known as a frame store unit captures the video and audio portions of a presentation. Each of these locations serves a small group of subscribers. The function of each frame store unit is to capture the video frames destined for subscribers assigned to the particular frame store unit. The frame store unit captures a video frame bearing the address of an assigned subscriber and converts the frame into a form it can store. Next, the frame store unit determines which audio message to associated with the video frame, bundles the audio and video together by time multiplexing the video on one channel and frequency multiplexing the audio on another channel, and then injects the result into he CATV feeder cable. The composite signal transmitted by the frame store unit appears as a standard television picture on the subscriber's television.
The audio and video signals processed by the frame store unit are in analog format. This is in sharp contrast to the presentation player of the present invention which receives and processes both the video and audio portions of a presentation in digital format. Moreover, the presentation player time multiplexes both the video and audio on a single channel.
The advantages of the presentation player over the frame store unit are numerous. The presentation player makes it possible for the interactive communication system to service more subscribers than the prior system because both the audio and video signals are time multiplexed on one channel. Moreover, the digital processing of these signals results in improved distortion immunity, improved audio fidelity, and an improved capability to maintain the integrity of the video portion of a presentation. An additional advantage of digital processing is an increase in the portion of the CATV frequency spectrum usable for transmission of the proposed audio/video service.
Thus, the digital processing and time multiplexing of both audio and video by the presentation player offers significant advantages over the frame store unit used in other interactive communication systems.